Bionic Transmission

Inside GM's stronger, faster 4L65-E transmission

Think of the 4L65-E transmission as the Steve Austin of GM's automatic overdrives. It looks like a standard 4L60-E, but beneath the skin, standard parts were replaced with improved components.

"We can make it stronger," said the Hydra-Matic engineers. "We have the technology."

Actually, the technology has always been there, and you many not have known, but the 4L65-E, or "L65" as GM's engineers call it, has been around for a little while, too.

Simply put, the L65 is a heavier duty version of the L60, which was the automatic found in the F-car, and currently, the Corvette and some light duty trucks. It's standard equipment in 6.0L truck applications, such as the Cadillac Escalade AWD, with an engine torque rating of 380 ft-lb (the 4L60-E's torque rating in the Corvette is 360 ft-lb).

An automotive application of the L65 was tuned recently in the high-performance HSV vehicles of GM's Australian Holden unit. These are rear-drive, LS1-powered cars, including the Holden Monaro coupe (reskinned as the new GTO), are considerably lighter than hulking Escaldades. Consequently, the car version of the L65 has a torque rating closer to 400 ft-lb, according to Steve Ford, GM's assistant chief engineer for the 4L60 and 4L80 transmissions.

"The L65 is stronger all around," says Ford. "Although it was initially developed for truck applications, the gearing we've developed for automotive duty cycles makes it a great performance upgrade. Right out of the box, it can handle about 20 percent more torque than the L60."

GM Performance Parts has released the 4L65-E as an over-the-counter item (PN 24221888), hoping to lure enthusiasts with older vehicles to the benefits of the electronically controlled overdrive transmission, as well as offering late-model Z28 and Corvette enthusiasts a stronger alternative to the stock 4L60-E.

The use of five-pinion gears for the input and reaction gearsets spreads the torque load so that less of the load is held by any one gear. The L65's gears also are made of powdered metal, which GM claims allows for more precise detail and accuracy of the part, as well as higher overall strength. (In these GM transmissions, the input and reaction gearsets are comprised of a sun gear, planetary gears, and a ring gear.)

Additionally, a heavy-duty, needle-type thrust bearing replaces a thrust washer for the interface between the reaction shaft and the reaction sun gear and shell.

Increasing the strength of the stator shaft came from heat treating the shaft's splines (which mesh with the hub of the stator roller clutch), and substituting the L60's steel-backed bronze bushings with stronger aluminum versions.

Also in the L65, the turbine shaft (the main component transferring torque from the converter into the transmission) is strengthened through induction hardening. Compared to heat treating, which involves a heating/cooling cycle to improve hardness and strength, induction hardening utilizes an electric current in the heating/cooling cycles.

Another improvement specific to the L65, is the use of larger-diameter rollers in the roller clutch. They better handle the increased loads of the L65, as do the seven friction plates of the 3-4 clutch. The L60 has only six friction plates for the 3-4 clutch; adding a seventh plate creates higher shift energy capacity.

Hydra-Matic engineers also improved the output shaft's capacity through shot-peening. The process involves concentrating the peening in several high-stress areas of the output shaft, thereby producing a longer fatigue life.

Despite these upgrades, the L65's gearing remains the same as the L60's: 3.059 for first gear, 1.625 for second, 1.000 for third and .0696 for the overdrive.

Finally, the L65's valve body, including line pressure and shift timing, differs from the L60 by optimizing shifts based on a higher engine torque curve. Also, to withstand the higher fluid pressure of the L65, the springs in the accumulator valve are stronger than those in the L60.

Shift points for the L65 are programmed to complement the Corvette Z06 LS6 engine's powerband and, compared with the 4L60-E, the maximum shift speeds for each gear change is lowered from 6,100 rpm to 5,600 rpm.

"Although the 4L65-E was originally developed for trucks, the transmission available through GM Performance is specifically tailored to cars," says Ford. "We think it offers the best compromise to a five-speed manual. It's got great strength and the gear ratios complement a car's power-to-weight ratio."

Making it Fit All the improvements made to the 4L60-E to make the 4L65-E are internal, so it will bolt up to any vehicle originally equipped with the 4L60-E. And since the L60/L65 transmissions are basically electronically controlled versions of the 4L60 (which was known as the 700R4 until the early '90s), they'll bolt up to most GM vehicles from the early '80s and up.

Of course, the 4L65-E requires the use of an electronic controller, whereas the non-electronic versions of the L60 or 700R4 do not. These non-electronic overdrive transmissions, however, were used in computerized applications and adapting them to carbureted, non-computer vehicles requires the use of a throttle valvespring and some "just right" adjustments to ensure proper kickdowns.

That's not the case with electronically controlled transmissions like the L65. Swapping it into an older vehicle, though, requires the use of its electronic controller. And if the swap is performed with a carbureted vehicle, an aftermarket controller kit with a specialized throttle position sensor is a must. Aftermarket vendors, such as JET Performance (www.jetchip.com) or Phoenix Transmission Products (www.phoenixtrans.com) offer such kits.

Here are a few additional transmission swap considerations: * The two-piece case of the 4L65-E is bulkier than, say, a TH350 or TH400, which means the transmission tunnel may need massaging. * The L65 is relatively long (approximately 3 inches shorter than a TH350), therefore a custom driveshaft may be required. * Depending on the vehicle, a new rear crossmember may be required to mount the tail end of the transmission * Because the L65 uses an electronic signal to indicate vehicle speed, a mechanical speedometer won't work without a signal converter, such as Abbott Enterprises' Cable X (see sidebar story).

GM supplies the torque converter with the L65, and most shift linkages from older GM vehicles can be made to work with it. In fact, several aftermarket companies, such as Shift Works (www.shiftworks.com), offer conversion kits to adapt stock-type shifters of many '60s-vintage Powerglide applications to modern GM transmissions. Year One offers similar products.

When ordered through a GM dealership, the 4L65-E has a list price of $2,595, not including the necessary controller. We're told an inclusive kit is on the way, but in the mean time, you'll have to use the L60 controller (PN 12497316).

Yes, you could probably upgrade an L60 for less, but we think the thoroughness of 4L65-E's revisions make it an attractive alternative. It also offers the benefits of being brand new and warranted.

Besides, you can tell everyone who asks that you've got the "Bionic Transmission."

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The built-in improvements that comprise the 4L65-E include this collection of components: hardened stator, turbine, and output shafts, five-pinion input and reaction carriers, and 3-4 clutch pack with an additional friction plate (seven versus the 4L60-E's six plates).

The biggest change to the L65, when compared to the 4L60-E, is the replacement of four-pinion input and reaction carriers with these five-pinion gearsets. This change strengthens the transmission by reducing the load on each of the gears.

Here, the input sun gear rests in the L65's new five-pinion input carrier. Like the reaction carrier, five sun gears are stronger because, compared to the L60's four gears, the load on each of the gears is reduced.

The L65's turbine shaft, which is driven by the converter's turbine as fluid from the impeller is splashed on it, is induction-hardened. Similar to heat treating, induction hardening introduces an electric current during the heating/cooling process.

The stator is the reaction (stationary) member of the torque converter for torque multiplication. It controls fluid flow from the impeller in the reduction phase of the converter's operation. To handle its increased torque capacity, the 4L65-E's stator shaft splines are heat treated in order to increase their strength.

For stronger 3-4 shifts, the 4L65-E's 3-4 clutch pack has seven friction plates. The 4L60-E's 3-4 pack has only six plates.

What about the 4L80-E and L85? Yes, the 4L80-E and 4L85-E offer the same electronic controlled advantages of the L65 and L60. After all, the L80 and L85 boast 440 ft-lb and 460 ft-lb torque capacities, respectively.

And, yes, the L80 and L85 are direct descendents of the venerable Turbo 400--which is, of course, merely a heavy-duty, longer version of the Turbo 350. So, they should fit, right?

The L80 and L85 will fit were Turbo 400 have gone before, but if you're running a small-block the L65 or L60 is the way to go, says Jim La Fontaine, lead systems engineer for transmissions at GM's Performance Division.

"The L80 and L85 are better suited to big-block applications," says La Fontaine. "The L65 is suited to small-block engines; it's designed to fit with the drivetrain of a small-block-powered vehicle to make installation relatively simple."

The L65 has another important advantage over the L80: it's a lot lighter. A 4L65-E weighs about 55 pounds less than an L80 or L85.

Cable X Abbott Enterprises' quick fix for using an electronic transmission with a mechanical speedometer

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Abbott Enterprises, of Pine Bluff, Arkansas, has a solution to the dilemma of the use of an electronic transmission and a mechanical speedometer. Its Cable X converter transforms the electronic signal of the transmission into a motor-driven output that drives a traditional mechanical speedometer.

The $300 Cable X is a box with electronic connections on one side and a mechanical cable hook-up on the opposite side. A motor inside the box turns the speedometer cable based on the signals received by the electronic transmission.

"It's an easy install," says Abbott's John Ware. "There are just three wires for the transmission and simply the cable hook-up for the speedometer."

Ensuring the speedometer's accuracy falls to adjustable dip switch settings on the Cable X box, which calculate the correct number of pulses per mile based on the transmission gear (number of teeth), axle ratio and tire size. Abbott Enterprises says the device is accurate to 2 percent of the transmission's electronic signal.

Simple also describes the idea to bring the Cable X to the enthusiast market. Previously, Abbott Enterprises' existence depended solely on the trucking industry. The company manufactures a variety of tachographs and other speed/timing equipment for the over-the-road crowd. But the growth of GPS navigation and tracking cut into Abbott's core business.

"We had a couple of car enthusiasts at the company who suggested the Cable X would be great for older cars using modern transmissions," says Ware. "Frankly, we didn't think there would be much of a market for that application, but the phones haven't quit ringing. The response has been terrific."

History of the L60-Series Transmission Today's 4L65-E and 4L60-E transmissions trace their lineage to 1982 and the introduction of the 700R4, one of General Motors' first production automatic overdrive transmissions.

Two versions of the 700R4 appeared: one with a 60-degree bellhousing bolt pattern and another with a 90-degree bolt pattern. And though the advantages of lower cruising rpm and higher fuel economy were widely praised, the early 700R4s suffered from weaknesses that caused many to fail in even the lightest-duty applications.

By the '87 model year, the 700R4 had been internally upgraded and the problems that plagued earlier versions of the engine disappeared. In the '90s, the name changed to 4L60, reflecting GM's new nomenclature for all its transmissions--"4" for four-speed, "L" for longitudinal (rear-wheel drive), "60" denoting the torque capacity rating. (The "E" was added when the transmission was converted to electronic control.) The 700R4 and 4L60 are internally similar, including gearing.

The 4L60-E came along in the mid-'90s, and shortly thereafter its design was changed from a three-piece construction to a two-piece design. Currently, the L60 and L65 have a separate, 360-degree bellhousing, which completely encloses the torque converter. This was done to increase powertrain stiffness and reduce vibration.

The electronic versions of the transmission also use an electronically controlled capacity clutch, instead of a mechanical lock-up clutch. This design lets the computer decide on the necessary amount of slip, which maximizes fuel economy.

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